The present invention relates to cemented carbide seal rings for potable water applications satisfying new demands of Fe, Ni and Cr contents.
In the description of the background of the present invention that follows reference is made to certain structures and methods, however, such references should not necessarily be construed as an admission that these structures and methods qualify as prior art under the applicable statutory provisions. Applicants reserve the right to demonstrate that any of the referenced subject matter does not constitute prior art with regard to the present invention.
Cemented carbide for corrosion resistance demanding applications such as seal rings, bearings, bushings, hot rolls, etc. generally has a binder phase of Co, Ni, Cr and Mo, where the Cr and/or Mo addition act as corrosion inhibitors. An example of such a cemented carbide is disclosed in U.S. Pat. No. 4,497,660.
U.S. Pat. No. 6,010,283 and related patents disclose a cemented carbide with Coxe2x80x94Nixe2x80x94Fe binder phase with 40-90 wt. % Co and 4-36 wt. % of each of Fe and Ni.
In cemented carbide seal rings for potable water applications Co and Ni-based binder phase cannot be used because of insufficient corrosion resistance. Instead cemented carbide with binder phase based on Ni and Cr have to be used. In the newly approved British standard BS6920, a cemented carbide to be used in potable water applications must have a content of Fe, Ni and Cr of less than 50 xcexcg/l of each, as measured in a leach test with deionized water at 85xc2x0 C. must be fulfilled, which is not possible with presently used cemented carbide seal rings.
It is therefore an object of the present invention to provide seal rings for potable water applications fulfilling the demands of BS6920.
It has now surprisingly been found that a cemented carbide with a binder phase combining Fe, Ni, Co, Cr and Mo gives significant improvement in corrosion resistance. This cemented carbide material possesses a corrosion resistance on the order of stainless steel when placed in hot water. Thus, the cemented carbide of the present invention is able to satisfy the demands of BS6920. As a result the corrosion resistant cemented carbide can be used in seal rings in potable water applications according to BS6920. Thus a seal ring with the corrosion properties of stainless steel but with the wear resistance of cemented carbide is obtained.
According to the present invention there is now provided cemented carbide seal rings consisting of at least one hard phase in a binder phase based on Co, Ni and Fe fulfilling the requirements of BS6920.
According to one aspect, the present invention provides a corrosion resistant carbide seal ring comprising a hard phase and a binder phase, the ring having a high resistance to leaching such that less than 50 xcexcg/l of each of Fe, Ni and Cr leaches into deionised water at 85xc2x0 C. when subjected to the procedure set forth in British Standard BS6920, Section 2.6, 1996.